I have played around with HFTA using terrain files that I manually
generated by simply editing an existing file to create cliffs and sharp
ridges. It's very easy to do and comes up with interesting results,
although I can't speak to their validity.
One interesting experiment is to create a terrain object that is not
symmetrical ... for example gentle upward slope on one side and sharp
decline on the other side. The results for low angles are of course
different depending upon the incident side, which I have always felt
could contribute to the fairly uncommon "one way skip" that I and others
seem to have experienced.
A significant limitation of HFTA, though, is that it won't show RF at
any angle below zero elevation even if you have a 2,000 foot tower.
Dave AB7E
On 3/4/2024 1:15 PM, Leeson wrote:
I still think of the foreground slope concept as "Moxon Slopes," from
the work and publications of Les Moxon, G6XN, who was a great personal
inspiration to me.
An interesting related question for which I don't find many references
is the HF propagation over a foreground knife-edge ridge that, while
lower than the antenna that "sees" over it, is close and high enough
to block ground reflection angles up to, say, 12-15°. This includes
the complication of diffraction as well as ray tracing. A start is "HF
Terrain Assessment" by KR7C, see especially pp. 15-18,
https://k0rv.files.wordpress.com/2015/01/hf-terrain-analysis.pdf
I think the pattern above the ridge, after giving effect to
diffraction, is pretty much the same as without the blockage, with
"diffraction wiggles" at the point it hits the ridge. But from that
elevation angle down to the horizon it seems the lack of ground
reflection denies the 6 dB potential gain, but removes the
cancellation at the horizon, yielding a regime more like the
free-space pattern of the antenna.
For an antenna high enough to see over a ridge, it will typically be
high enough to have a substantial number of nulls, once it finally can
clear the blockage angle. Any additional comments, techniques and
references would be appreciated.
Here are some additional online references that may be of interest in
the general subject of ground reflection and slope.
M. Weissberger, et al., "Radio Wave Propagation: A Handbook of
Practical Techniques for Computing Basic Transmission Loss and Field
Strength," 1962, https://apps.dtic.mil/sti/tr/pdf/ADA122090.pdf
P. D. Rockwell, "Station Design for DX, Part I -- Antenna Topics and
Siting," QST, Sept 1966, pp. 50-54,
https://www.rfcafe.com/references/qst/station-design-dx-september-1966-qst.htm
G. Hagn, "HF Receiving Antenna Directivity Patterns and Gain for
Ionospheric Propagation Model Predictions for Short-Wave
Broadcasting," IEEE Trans Broadcasting, Volume 34, Issue 2, June 1988,
pp. 221-229, https://ieeexplore.ieee.org/document/1439
J. K Breakall, et al., "The modeling and measurement of HF antenna
skywave radiation patterns in irregular terrain," IEEE Transactions on
Antennas, Volume 42, Issue 7, July 1994, pp. 936-945,
https://ieeexplore.ieee.org/document/299595
R. D. Straw, "What I've Learned in Two Decades of Terrain Assessment
by N6BV," video, 2013, https://www.youtube.com/watch?v=D6nRpeVseSc
R. D. Straw, "Terrain Assessment for HF Contesting," 2014,
https://seapac.org/seminars/2014/sea-pac2014-n6bv-Terrain%20Assessment.pdf
D. B. Leeson, "Match HF Antennas to the Ionosphere & Terrain," 2017,
https://www.dropbox.com/s/hhc00iy6t4h509c/Ionospheric%20Radio%20REDXA_sm.pdf?dl=0
D. B. Leeson, "Siting and Installation of Yagi Antennas," Ch. 10 in
"Physical Design of Yagi Antennas," 1992, available online at
https://www.dropbox.com/s/hmhkeofz0igrg1e/Physical%20Design%20Of%20Yagi%20Antennas%20D%20B%20Leeson%20V2.pdf?dl=0
73 de Dave, W6NL/HC8L
On 3/3/24 4:43 PM, Brian Beezley wrote:
Just a note that Rudy Severns, N6LF, has put all 35 of his published
Antenna Compendium, Communications Quarterly, NCJ, QEX, and QST
articles in one place. Each article is a PDF file in magazine format.
So much good stuff. Just click on the article you want:
https://www.antennasbyn6lf.com/
The reference I gave to his original soil parameter article was
actually to a preliminary version. Here's the final article:
https://rudys.typepad.com/files/qex-nov-dec-2006-soil-parameters-at-hf.pdf
The article N6RK mentioned about determining ground parameters with a
low dipole is here:
https://rudys.typepad.com/files/qex-nov-dec-2016-soil-characteristics-using-low-dipole.pdf
Brian
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